The Swedish Meteorological and Hydrological Institute (SMHI) has been working over the past several years to automate weather stations for the collection of meteorological data. Although most of these stations rely on a fixed connection to SMHI's data network, a number of stations. In remote areas have been configured for wireless data communications. Swedish network operator Telia Mobitel's Mobitex network and a measurement solution from Finnish supplier Vaisala are key compo-ents in this application.

Weather reports without wires

In Sweden, as in most countries, weather stations are distributed evenly throughout the country, with additional stations located in meteorologically important areas. Critical areas in this regard are coastlines, mountain ranges and other areas where large differences in temperature and other conditions can be expected to produce rapid and substantial changes in the weather.

The data collected at weather stations consists of standard measurements such as temperature, barometric pressure, humidity, wind speed and direction and precipitation. This data can be recorded by standard instruments. Other data, such as cloud cover and ceiling, are typically estimated by human observers but can also be measured by instruments.

While the accuracy and reliability of the data collected at each weather station are obviously important in producing good forecasts, compiling data frequently and regularly from a large number of locations is crucial for forecasting the weather. With some 160 weather stations throughout the country, data collection is thus a major challenge for SMHI.

OBS 2000 project

In the past, SMHI, like many of its counterparts in other countries, has relied on manual weather stations with operators who report in by phone or radio at regular intervals, typically every three hours around the clock. With increasing demands on the weather service, however, it has been necessary to deploy a greater number of automatic weather stations and to increase the frequency of data collection.

"We began planning the transition to automatic weather stations as part of the OBS 2000 project in 1991," relates SMHI's project manager Britt Frankenberg. "By 1994, we had 13 test stations in operation. Today we have a total of 115 automatic stations, but there are still 45 manual stations in operation."

Advancing technology

The manual stations and human observers are being eliminated. "This is an inevitable consequence of the requirements imposed on us by the government," notes Britt. " Each manual weather station needs the equivalent of 1,3 full-time employees for its operations. By automating weather stations, we have been able to meet government requirements and improve efficiency by 20 percent, compared with 1991.

Reliability a must

Björn Hansén is a service engineer who has been involved in the OBS 2000 project since the start. He and several colleagues are responsible for the maintenance of SMHI's automatic weather stations, a job that keeps Björn on the road three to four months a year.

"Our first choice for wireless data communications was Mobitex," says Björn. "Mobitex is more reliable than cellular systems and costs less because traffic charges are incurred only for the number of data packets, not the connection time. For SMHI, it is also important that the Swedish Mobitex network is certified by the military for use in national emergencies."

The service engineers normally visit the automatic stations once a year to perform preventative maintenance. When Mobile Data Magazine accompanied Björn to a Mobitex station on an island outside the city of Karlskrona in southern Sweden, there was little to do apart from replacing a few cables and making minor adjustments. Despite harsh weather conditions, the radio and measurement equipment had held up well during the winter.

Part of the network

In addition to the 160 weather stations around the country, SMHI receives meteorological data from many other sources. It should therefore come as no surprise that SMHI operates one of Sweden's largest data networks or that the agency maintains some of the country's largest databases.

Providing a gateway to the mainframe data-bases from the Mobitex stations was a task for which B & M Systems was given responsibility. The basic task on the host-side was to create a Windows-based application that mediates between the mainframe system. Data collected from the Mobitex stations is passed on to the mainframe databases. Likewise, control information for reconfiguring the station is passed down from the mainframe to the host PC and then on via Mobitex to the remote weather station.

"Our MobiWin software provides a Mobitex driver that sits beneath the Windows application, which we developed using the MobiWin SDK," relates Per Bergström, project manager at B&M Systems. "We then implemented an interface on top of the application that uses remote procedure calls (R PC) to communicate with the mainframe DBMS. To the mainframe, the Mobitex weather station looks like just another dial-up client."

Compelling advantages

As the SMHI application illustrates, Mobitex has a number of other compelling advantages. Above all, the system is very reliable. Because of the redundancy inherent in a packet-switched network, data collected at the station will nearly always be forwarded, even when natural disasters, such as hurricanes or earthquakes bring down other communications networks. This is an important criteria for national weather services whose responsibilities include continuing to function when disaster strikes.

Perhaps a sudden shower may not be a disaster for vacationers on their way to the beach. For other groups, such as farmers, whose livelihood depends on the weather, advance warning of torrential rain or crop-killing frosts can make a major difference. With Mobitex, meteorologists may still not be able to do anything about the weather, but they can gather the essential information for their forecasts in more remote locations.

Automatic weather station features

Central to SMHI's automatic weather station installations in remote locations is a measurement solution from Finnish equipment supplier Vaisala. The company, which has its head office in Helsinki and sales office and dealers throughout the world, specializes in measurement systems for meteorology, the environmental sciences, traffic safety and industry.

The product used in SMHI's stations is the Milos 500 data collection and processing system. The system is based on a 16-bit 80C 188EB static CPU and a multitasking real-time operating system (RTOS) and is designed to meet military specifications. The system board can be used with a number of expansion boards to support virtually any sensor configuration and all common data communications protocols.

The basic Milos 500 system consists of a Central Processing Unit, a Sensor Interface Unit, and a Switched Power Supply Unit.

A modular software package called "Your Way" has been designed especially for Vaisala's automatic weather data collection systems. The software runs on the Milos 500, as well as any IBM-compatible PC, and contains all the functions needed to configure a customized data collection system. Programming knowledge is not required. Extensive editing, trace and debugging tools are included.

The sensor and device setting, command sets, measurement algorithms, calculations, interrupts, communications and report formats can be selected from a predefined parameter library. The Your Way configuration program guides the user through the setup procedure using full-screen menus and online help screens. The parameter files thus created can be downloaded directly from a PC to the Milos 500 over a serial interface line or via PC Card memory cards.

Vaisala developed Mobitex software for the Milos 500 system with the help of B&M Systems of Uppsala, Sweden, which also developed the gateway software for the host system in SMHI's application. Because the Milos 500 uses a proprietary RTOS, Vaisala worked with B&M Systems to develop a platform-specific version of the native Mobitex MASC protocol for the Milos 500. This makes the software on the terminal side very efficient and allows virtually all Milos 500 parameters to be remotely configured over Mobitex.